Differences
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| Both sides previous revision Previous revision Next revision | Previous revision | ||
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x264_quality [2014/08/17 15:36] beandog |
x264_quality [2014/08/17 15:47] (current) beandog |
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| Use SSIM or PSNR to gauge differences between encoding settings. | Use SSIM or PSNR to gauge differences between encoding settings. | ||
| + | |||
| + | ==== SSIM ==== | ||
| When comparing two values, here is the formula to discern what percentage amount something has improved. | When comparing two values, here is the formula to discern what percentage amount something has improved. | ||
| Line 37: | Line 39: | ||
| Here's the formula: | Here's the formula: | ||
| <code> | <code> | ||
| - | (((1 - [old SSIM]) / (1 - [new SSIM])) - 1) x 100 | + | (((1 - old) / (1 - new)) - 1) * 100 |
| </code> | </code> | ||
| + | |||
| + | Here's a simpler visualization: | ||
| + | |||
| + | <code> | ||
| + | 1 - 0.9613678 = 0.0386322 | ||
| + | 1 - 0.9751283 = 0.0248717 | ||
| + | 0.0386322 / 0.0248717 = 1.55325932686547361057 | ||
| + | 1.55325932686547361057 - 1 = 0.55325932686547361057 | ||
| + | 0.55325932686547361057 * 100 = 55.325932686547361057 | ||
| + | </code> | ||
| + | |||
| + | Rounding it out to an integer, would be 55, for a result of 55%. So when encoding this particular video at double the bitrate, the SSIM increases by 55%. Not bad! | ||
| + | |||
| + | Here's a PHP function to do the same thing: | ||
| + | |||
| + | <code> | ||
| + | function ssim_improvement($old_ssim, $new_ssim) { | ||
| + | |||
| + | $a = 1 - $old_ssim; | ||
| + | $b = 1 - $new_ssim; | ||
| + | |||
| + | $c = $a / $b; | ||
| + | |||
| + | $d = $c - 1; | ||
| + | |||
| + | $e = $d * 100; | ||
| + | |||
| + | return $e; | ||
| + | |||
| + | } | ||
| + | </code> | ||
| + | |||
| + | === PSNR === | ||
| + | |||
| + | Using the doom9 forum post as a reference, the equation is: | ||
| + | |||
| + | <code> | ||
| + | (new - old) / 0.05 = % improvement | ||
| </code> | </code> | ||
